A new grouting material called Neutrogel® that has minimal impact on soil and groundwater, a much lower carbon footprint and lower costs, has been successfully used on a Keller project for the first time. 

Keller's using Neutrogel, a new greener grout, on a project in Germany

Keller is constantly innovating to find new and more sustainable products and technologies, and the latest comes with the launch of Neutrogel® - the first ever pH neutral sodium silicate-based grout, making it completely harmless when it’s in the ground.

“Chemical grouts typically make groundwater highly alkaline, which can have a negative impact on micro-organisms in the soil,” explains Paul Pandrea, Keller’s European Technical Director. “Older mixes, which are increasingly prohibited, also contain harmful alumina and other heavy metals, which Neutrogel® doesn’t.

“And while cement bentonite jet grouting is effective for bottom seals, it produces spoil and the cement element means it has a significant carbon footprint. Neutrogel® is a liquid solution that penetrates the pores in the ground, so uses a lot less material. It therefore has a much smaller carbon footprint – about 1/10th of CO2 than the equivalent jet grouting solution – and produces no spoil.”

Perhaps most importantly for commercial applications, because it uses less materials, it can be around a third cheaper, which is likely to make it a very attractive option for clients. 

A proven success

Neutrogel® took Keller a year to develop and after successful trials secured technical approval for general use by the German Institute for Construction Technology (DIBt). A patent is pending.

It was used for the first time on a bottom seal project in 2020 on the site of a new building at the Karlsruhe Institute of Technology in Germany.

The scope called for Keller to install a deep-seated bottom seal with a footprint of 3,620m². The seal had a designed thickness of 1m and was to be located 3.3m below the excavation depth of 5.8m. To meet the specification, the finished seal had to allow a groundwater ingress of no more than 1.5 litres per second, per 1,000m² of exposed surface.

Due to Karlsruhe’s close proximity to the Rhein river, the ground was composed of a man-made fill between 2m and 2.7m, under which were silty, medium-dense sands, over dense to very dense gravels.

To get the Neutrogel® into the ground and create an impermeable seal, the team used bundles of three grouting tubes inserted at 1.5m intervals using a sheet pile driving rig. The installation tool itself was formed from a tube with four welded wings to provide guidance and increase stiffness.

The tubes were inserted at almost 2,000 separate points over two-and-a-half weeks, with the Neutrogel® pumped at around 10-15 litres per minute. In total the project required around 1.65 million litres, compared to an estimated 4.6 million litres of grout for a comparable jet grouting solution, and produced no spoil at all.

Spreading the word

“Although the process required several pumps working in parallel, the grouting process went very smoothly and produced very low permeability – approximately 0.15 litres per second per 1,000m² of exposed surface, well within the tolerance levels,” adds Paul. “So, technically and economically this first project was a huge success. Now the next step is to improve our mixing technology and pumping equipment, and look for more opportunities. We’ll also be promoting it to our clients, publishing technical papers and sharing our findings with the rest of the Keller global community.”

However, Neutrogel® won’t be replacing traditional jet grouting methods completely. That’s because, while it’s ideal for any application where you need to reduce permeability, it doesn’t provide much structural resistance (strength).

Even so, the potential for Neutrogel® is exciting. As cement-based products come under increasing scrutiny, Neutrogel’s efficacy and cost-savings could make it a very popular and much more sustainable alternative in the bottom seal market.

Karlsruhe Institute of Technology project - comparison of two different techniques  

  • Jet grouting: estimated CO2 ≈ 3400 equivalent tonnes
  • Neutrogel®: estimated CO2 ≈ 300 – 250 equivalent tonnes
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